03 Periodic Table

Introduction to the Periodic Table

• The periodic table is essential for understanding chemistry.
• It organizes all known elements in the universe.
• Elements are the building blocks of matter, like Lego bricks.
• Combining elements in different ways creates different substances with unique properties.
• Each square on the periodic table provides information about an element.
• The name of the element (e.g., mercury) is given.
• The atomic number indicates the number of protons in the nucleus. For mercury, it's 80.
• The atomic number differentiates elements.
• The symbol (e.g., Hg for mercury) often comes from Latin names.
• The average atomic mass is the weighted average mass of isotopes of an element.
• Electronegativity indicates how strongly an atom attracts electrons.

Reading the Periodic Table

• Hydrogen (H) is in the upper left corner with an atomic number of 1.
• The table is read left to right.
• Helium (He) is element number 2, located on the far right of the first row.
• The table continues reading from left to right, skipping spaces.
• The table layout reflects how electrons fill orbitals around the atom.

Atomic Structure Basics

• Atoms have a nucleus with a positive charge and electrons orbiting it.
• Electrons are not like planets orbiting; they behave as waves.
• In a hydrogen atom, one proton in the nucleus is balanced by one electron.
• Atoms are neutral because they have equal numbers of protons and electrons.
• The atomic number indicates the number of protons (and electrons in a neutral atom).
• Helium, with an atomic number of 2, has 2 protons and 2 electrons.
• Phosphorus (atomic number 15) has 15 protons and 15 electrons in a neutral atom.
• Tungsten (atomic number 74) has 74 protons and 74 electrons.
• Nucleus also contains neutrons, which contribute to mass but have no charge.
• Neutrons are important in nuclear reactions but not chemical reactions.
• Chemical reactions involve the transfer and sharing of electrons.

Metals, Non-metals, and Metalloids

• The left side of the periodic table contains metallic elements.
• Metals are typically good conductors of electricity and heat.
• Metals are ductile, meaning they can be drawn into wires.
• The right side contains non-metallic elements.
• Non-metals are often brittle and poor conductors.
• A staircase-like line divides metals from non-metals.
• Elements near the staircase have characteristics of both metals and non-metals.
• Silicon (Si) is used in computer chips because it can act as a conductor or insulator.
• Germanium and gallium are also used in computer chips.
• Carbon is essential for life and can form long chains, like DNA.

Periodic Table Overview

• The periodic table is ordered by atomic number.
• Each element has a specific number of protons in its nucleus.
• A neutral atom has an equal number of protons and electrons.
• The nucleus also contains neutrons, which contribute to the element's mass.
• Atomic mass is listed on the table.

Origin of Elements

• Many elements, including hydrogen, helium, and some lithium, originated from the Big Bang.
• Elements up to iron (Fe) are formed through nuclear fusion within stars.
• Fusion in stars involves gravity compressing hydrogen, leading to the creation of heavier elements like helium.
• This fusion process continues until iron is formed, beyond which stars cannot create heavier elements through fusion alone.

Formation of Elements Heavier Than Iron

• Supernova explosions and neutron star collisions are responsible for creating elements heavier than iron.
• These cataclysmic events provide the necessary conditions for the formation of elements with more protons than iron, such as cobalt, zinc, silver, mercury, and gold.

Stellar Cycle and Element Creation

• The universe undergoes a cycle where stars are born, die, and explode, leading to the creation of heavier elements.
• Our solar system has likely experienced multiple cycles of stars exploding and re-coalescing, as evidenced by the presence of elements like gold and lead within it.

Organization of the Periodic Table

• The lanthanide and actinide series are typically placed below the main body of the periodic table for space-saving reasons.
• These series actually fit within the main table, pushing the elements to the right.

Radioactive Elements

• The heaviest elements, such as element 118, are radioactive due to their large nuclei.
• The nuclear force in these heavy elements is not strong enough to hold the nucleus together, leading to radioactive decay.
• These heavy elements are often created in particle accelerators, but they are unstable and decay rapidly.

Focus of Chemistry

• Chemistry primarily focuses on the elements in the top half of the periodic table due to their stability.
• Organic chemistry is primarily concerned with carbon, nitrogen, oxygen, and hydrogen.

Key Features of the Periodic Table

• There are about 100 known elements, with 118 currently listed on the periodic table.
• Elements are ordered by atomic number, representing the number of protons in the nucleus.
• The symbols for some elements are derived from their Latin names.

Importance of Organization

• Organizing the periodic table by atomic number reveals that elements in the same column have similar chemical properties.
• Elements in the same column tend to gain and lose electrons in similar ways, allowing for easier prediction of their chemistry.

Molecules

• Atoms can bond together to form molecules.
• A molecule is formed when two or more atoms are chemically bonded.
• Examples of molecules hydrogen (H2), oxygen (O2), and chlorine (Cl2).

Compounds

• A compound is a type of molecule consisting of different elements bonded together.
• Water (H2O) and carbon dioxide (CO2) are examples of compounds.
• Molecules consisting of the same element, such as O2, are not considered compounds.

Representing Molecules

• Molecules can be represented using chemical symbols and subscripts to indicate the number of atoms of each element.
• They can also be depicted as balls connected by sticks, representing the atoms and chemical bonds.

Chemical Bonding

• Atoms bond together by sharing electrons due to the strong electric force.
• The shape of molecules, such as the bent shape of water, influences their properties.

Properties of Elements vs. Molecules

• The properties of a molecule can differ significantly from the properties of the elements that compose it.
• Water (H2O) is a liquid at room temperature, while hydrogen and oxygen are gases.
• The boiling point and flammability of water also differ from those of hydrogen and oxygen.
• Combining elements can result in new compounds with unique and unexpected properties.

Chemical Symbols and Elements

• Chemical symbol for sulfur is S
• Gold's symbol is Au, derived from a Latin word
• Gold as element number 79 has 79 protons and 79 electrons
• Potassium's symbol is K, from the Latin word "callium"
• Potassium is element number 19
• Chlorine's symbol is Cl
• Copper's symbol is Cu, and is element number 29
• Uranium's symbol is U
• Nickel's symbol is Ni
• Sodium's symbol is Na, from Latin (element is highly reactive in water)
• Aluminum's symbol is Al
• Silicon's symbol is Si, and is element number 14

Elements vs. Compounds

• Calcium chloride (CaCl2) is a compound, not an element
• Elements are the basic building blocks of matter that cannot be divided further and retain their characteristics
• A sample of sulfur atoms is an element
• Compounds consist of two or more elements bonded together

Cytosine and DNA

• Cytosine, a part of DNA, contains hydrogen, carbon, nitrogen, and oxygen
• Because cytosine contains multiple elements, it is a compound

Periodic Table Organization

• The periodic table is organized by increasing atomic number
• Atomic number is the number of protons in the nucleus
• Each element on the periodic table has a name and a symbol
• The left-hand side of the periodic table consists mostly of metals
• The transition region (the "staircase") contains elements with characteristics of both metals and non-metals
• Elements in the same column of the periodic table have similar properties
• Elements in the same column gain and lose electrons in a similar way